With increasing popularity of mobile voice and data communication, there is an ever increasing demand for high-speed voice and data communication. The licensed spectrum for cellular communication is rapidly being exhausted by a dense and growing subscriber base. This applies in particular to the valuable low-frequency bands with low propagation loss traits.
A significant amount of unlicensed spectrum is available. For illustration, a significant amount of spectrum is globally available in the 5 GHz band. It is desirable to utilize the unlicensed spectrum, e.g. the LTE-unlicensed (LTE-U) spectrum, to augment the capacity of licensed frequency carriers. The unlicensed spectrum may be used for carrying data traffic for mobile services. The purpose of unlicensed spectrum usage is to extend cellular communication to unlicensed spectrum.
Carrier aggregation may be performed in which usage of unlicensed spectrum and licensed spectrum is combined. The licensed carrier may be a primary carrier, e.g. a LTE licensed carrier. The unlicensed carriers may be secondary carriers to which data traffic may be offloaded in the downlink or both in the uplink and in the downlink.
In Licensed-Assisted Access (LAA), transmissions on carriers of the licensed spectrum may be used for assisting unlicensed spectrum access. For illustration, LTE-U data transmissions may still be controlled by a primary carrier in the licensed spectrum.
Different challenges must be met in LAA. For illustration, interference with non-cellular technologies or with other secondary cells may make it necessary that an unlicensed carrier is reconfigured frequently. Signalling overheads associated with interference detection and carrier selection in the unlicensed band may be high, which reduces efficiency and increases network loads.
Further, there may be a potentially large number of carriers in the unlicensed band which the eNodeB may need to handle. The handling of such a large number of carriers may increase system complexity.